Solar thermal decomposition of zinc oxide: An initial investigation of the recombination reaction in the temperature range 1100-1250 K

We present an experimental and theoretical study that explores the zinc vapour and O₂ reaction under laminar flow conditions similar to those that may exist at the exit of a high temperature solar reactor used to decompose ZnO(s). The zinc vapour and O₂ reaction was experimentally studied in an electrically heated tubular furnace. A finite difference mass transfer model for laminar flow, which accounts for radial diffusion of the gases to the tube wall, was developed to help interpret the experimental results. We found that when the gas and wall temperatures are below the decomposition temperature of ZnO(s) but above the condensation temperature of Zn(g), the mass transfer rate of Zn(g) and O₂ to the reactor wall limits the oxidation rate of Zn(g). ZnO(s) decomposition experiments were also carried out in a concentrating solar furnace in order to establish the importance of the temperature of an inert gas used in a solar reactor on the zinc yield. We found that the gas temperature should be above the Zn(g) condensation temperature in the hot region of the reactor in order to avoid oxidation of zinc vapour before it enters the quench unit.